The copending application Ser. No. 845,845 is incorporated herein by reference. The field and background of the invention herein are the same as in the copending application but for the aspect which is mentioned below. The disclosure of the copending application is considered also included herein.
The seat back core of the copending application is intended to deflect under pressure which gives it great strength, the flexure being effected by resilience and being followed by recovery. Metal cores will assume permanent set if deflected.
Deflection increases with the length of the seat back core and in the cores intended for vehicles larger than the so-called compact cars this deflection may be undesirable. Even in smaller vehicles it may be desired to limit the deflection or prevent it entirely.
The invention solves these problems by the use of a relatively stiff reenforcing steel member that is incorporated into the core.
Given a core that is constructed in accordance with the teachings of the copending application, securing a reenforcing member to the core by suitable fastening means such as bolts passing through the core and clamping the member in place would be the obvious way of attaching the bar. This requires additional operations, weakens the core and may not have the desired effect because of necessity it is fastened at specific points.
The invention utilizes a method of making the core which is not obvious and which results in the inclusion of a steel structure member that is completely married with the core along its entire length. The bar is installed into the mold before the molding process takes place so that the plastic material flows around the bar and locks it in position. This cannot be done normally because of the difference between the modulus of shrinking of the plastic and the modulus of expansion and contraction of steel. The solution by the invention is an exquisite one that considers the structure of the resulting core and the manner in which the steel member is disposed in the core.
In the blow-molding of relatively large elongate members such as the seat core of the invention, shrinkage occurs to a high degree in the direction in which parison has been formed. Logically the parison is blown in the long dimension of the seat core. The shrinkage resulting during the curing of the molded object can be as much as 0.018 inch for each inch of length. Considering that a typical seat core will extend across the interior of a vehicle cab and have a length of 50 inches and more, the shrinkage can amount to nine tenths of an inch. Steel expands with heat and contracts with cold, but the contraction during the molding process is insufficient to match the shrinking of the resin.
Since it is essential that the steel reenforcing member be locked into the seat core, the problem of preventing the core from bowing seems insurmountable. According to the invention, the construction of the reenforcing member and the manner in which it is placed in the mold during the molding process obviates this problem by permitting the member to slide relative to the seat core during curing.
Prior art which is known comprises the references cited during the prosecution of the copending application and others which are mentioned in the specification of the said copending application. These include the following:
______________________________________ 3,669,496 Chisholm June 13, 1972 Class 297/445 3,334,941 Krasinski et al Aug. 8, 1967 Class 296/66 3,317,238 Smoll May 2, 1967 Class 296/69 3,742,995 Confer et al July 3, 1973 Class 150/.5 3,705,931 Confer et al Dec. 12, 1972 Class 264/89 3,869,239 Confer Nov. 30, 1972 Class 425/302 B ______________________________________